Video imaging to assess specularity

ABSTRACT

A method for virtual, three-dimensional modeling of a subject using a depth-imaging camera operatively coupled to a modeling computer. A brightness image and a coordinate depth image of the subject acquired from each of a plurality of inequivalent vantage points are received from the depth-imaging camera. An angle-dependent reflectance is determined based on the brightness and coordinate depth images acquired from each of the vantage points.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application62/192,280, filed Jul. 14, 2015 and entitled “VIDEO IMAGING TO ASSESSSPECULARITY”, the entirety of which is hereby incorporated herein byreference, for all purposes.

BACKGROUND

Recent advances in depth-imaging technology have enabled the developmentof compact, low-cost depth-imaging cameras for the consumer market.These depth-imaging cameras are available as stand-alone devices and ascomponents designed for integration into more complex devices andsystems. Some of the new depth-imaging cameras employ time-of-flight(ToF) imaging. The ToF imaging approach is precise and economical, butmay be prone to error when applied to problematic subject geometries andmaterial properties.

SUMMARY

One aspect of this disclosure is directed to a method for virtual,three-dimensional modeling of a subject using a depth-imaging cameraoperatively coupled to a modeling computer. In this method, coordinatebrightness and depth images of the subject are received from thedepth-imaging camera. The images are acquired from each of a pluralityof inequivalent vantage points. An angle-dependent reflectance isdetermined based on the coordinate brightness and depth images acquiredfrom each of the vantage points.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter. Furthermore,the claimed subject matter is not limited to implementations that solvethe disadvantages identified in this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows aspects of an example depth-imaging camera.

FIGS. 2A and 2B illustrate multipath reflection interference in ToFdepth imaging.

FIG. 3 shows aspects of an example modeling computer and a smartphonewith an integrated depth-imaging camera.

FIG. 4 shows aspects of an example home-theatre system with a peripheraldepth-imaging camera and modeling computer.

FIG. 5 shows aspects of an example head-mounted augmented-realitydisplay system with an integrated depth-imaging camera and modelingcomputer.

FIG. 6 illustrates aspects of an example method for virtual,three-dimensional modeling of a subject using a depth-imaging cameraoperatively coupled to a modeling computer.

FIG. 7 shows aspects of virtual, three-dimensional modeling of anexample subject.

FIG. 8 is a graph of an example bidirectional reflectivity-distributionfunction (BRDF) of a subject locus.

FIG. 9 illustrates aspects of correction of multipath reflectioninterference in ToF imaging.

DETAILED DESCRIPTION

This disclosure describes configurations and associated methods foraccurate surface mapping of real-world subjects via depth imaging. Morespecifically, the systems and methods described herein support ‘objectcapture’ (OCAP). OCAP is a term applied to the optical digitization of areal world object (a ‘subject’ herein). As depth-imaging systemsproliferate, high-fidelity OCAP is expected to become increasinglyubiquitous, driven in part by related technologies, such as 3D printingand holographic projection.

One impediment to reliable OCAP is the acquisition of a subject havingvariable optical and/or material properties. In ToF imaging, a highlyreflective subject locus can indirectly illuminate another locus,causing ‘multipath’ interference. More specifically, integration oflight received along different optical paths, but arriving at the samepixel, corrupts depth estimation. Closely analogous to multipathinterference in ToF imaging is the problem of reflection-inducedoverlapping patterns encountered using structured-light projection,another depth-imaging technique. Various methods to detect and/orcorrect for multipath interference have been advanced, but arecomputationally expensive and may not reverse all kinds of errors. Somemethods rely on scanning very small active illumination patchesdistributed over the subject; these methods may be limited by low lightpower (yielding noisy scans on low reflectivity subjects) or may requireundesirably long scan times (exposing motion blur). Othermaterial-related limitations, besides multipath interference and thelike, present challenges for OCAP. Another is the inability of nativeToF systems to resolve surface attributes—e.g., textures and othermaterial properties—for subsequent modeling in ray tracing applications.

The approach now disclosed uses a depth-imaging camera with activeillumination to capture both depth and brightness imagery while thecamera is moved around the subject, and/or, while the subject is movedaround the camera. Reflectivity is estimated as a function of imagingangle relative to subject features. The reflectivity information may beused to probe the surface properties of the subject, correct multipathinterference for better depth estimation, and/or alert the user thatpotentially problematic loci are present in a scene. A basic feature ofthe disclosed solution is a depth-imaging camera or registered cameraarray capable of recording both a depth image of the subject and acoordinate brightness image with pixel brightness proportional to theintensity of the probe light reflected back from the imaged locus.

The exploded view in FIG. 1 shows aspects of an example camera 10. Theterm ‘camera’ refers herein to any imaging component having at least oneoptical aperture 12 and sensor array 14 configured to image a scene orsubject 16. The camera may also include an imaging optic, such as a lens(not shown in FIG. 1), arranged forward of the aperture. The sensorarray of camera 10 includes a two-dimensional matrix of light-sensingsensor elements 18. In some implementations, the sensor elements may becomplementary metal-oxide semiconductor (CMOS) elements, but otherarchitectures are envisaged as well. Each sensor element may beintrinsically responsive to light over a broad wavelength band. Forsilicon-based sensor elements, the wavelength response may range from300 to 1200 nm. Microlens array 20 is optionally arranged over sensorarray 14 to provide a larger acceptance cone at each of the sensorelements, for increased collection efficiency.

Due to the broad wavelength response of sensor elements 18, one or morepassive filters 22 may be arranged in series with sensor array 14 andconfigured to limit the wavelength response of the sensor array. Thepassive filters reduce noise by excluding photons of wavelengths notintended to be imaged. An IR-imaging camera, for example, may include avisible bandstop filter. In implementations in which both visible andnarrow-band IR response is desired, a visible and narrow-band IRbandpass filter may be used. If configured also for color imaging,camera 10 may include a color filter array (CFA) 24 of color filterelements 26. The color filter elements may be arranged in registry withthe sensor elements of the sensor array. An example CFA may present aBayer pattern—i.e., a repeated tiling of 2×2 subarrays having twogreen-transmissive, one blue-transmissive, and one red-transmissiveelement in each subarray, for example. In this implementation, theintegrated response from the sensor array may be converted into afull-color image using a de-mosaicing algorithm. In implementations inwhich both visible and IR response is required at each sensor element,each of the color filter elements may be transmissive in the IR band ofinterest.

Camera 10 includes an electronic controller 28. The electroniccontroller may include processor logic and associated electronic memory.The electronic memory may hold instructions that cause the processorlogic to enact any operation, algorithm, computation, or transformationdisclosed herein. In some implementations, the processor logic may takethe form of an application-specific integrated circuit (ASIC) orsystem-on-a-chip (SoC), in which some or all of the instructions arehardware- or firmware-encoded. In general, the electronic controller maycontrol the electronic shutter of sensor array 14, which affects theresponsiveness of sensor elements 18 to incident light. The electroniccontroller is also configured to individually address each sensorelement 18 of the array, as described further below.

Camera 10 may be configured for brightness imaging, depth imaging, orboth. Accordingly, the term ‘depth-imaging camera,’ may refer herein toa camera configured for both depth and brightness imaging. Forbrightness imaging, sensor elements 18 are addressed so as to integratethe intensity of light received at each sensor element. The integratedintensity is then associated with the brightness of the portion of theimage corresponding to that element. The resulting ‘brightness image,’has a brightness value assigned to each of a plurality of pixelpositions, registered each to a corresponding locus (X_(i), Y_(i)) of animaged scene. A ‘color image’ is a brightness image in which brightnessis resolved for each of a plurality of individual color channels—e.g.,red, green, and blue.

For depth imaging, sensor elements 18 may be addressed somewhatdifferently. ‘Depth’ is defined herein as a coordinate that increaseswith increasing distance from aperture 12 of camera 10, in a directionparallel to optical axis A of the camera. In a ‘depth image,’ an arrayof pixel positions are registered each to a corresponding locus (X_(i),Y_(i)) of an imaged scene; the depth value Z_(i) indicates, for eachpixel position, the depth of the corresponding locus. To image depth,camera 10 makes use of a modulated emitter 32, which may include one ormore infrared (IR) light-emitting diodes (LEDs) or an IR laser.Electronic controller 28 modulates the emitter at a high frequency(e.g., 100 MHz) and synchronously addresses sensor elements 18. Fordepth imaging, the act of addressing the sensor elements may includeresolving a phase offset in the response of each sensor element relativeto the modulation of the emitter. In some implementations, a series ofobservations acquired in rapid succession may be used to determine thephase offset. In some implementations, the phase offset from each sensorelement may be converted into a pixel-resolved time-of-flight (ToF) ofthe modulated light—viz., from the emitter to a locus of the subjectimaged at that sensor element and then back to the sensor array. ToFdata may be converted into a depth coordinate and assembled into a depthimage of the subject. In combination depth- and brightness-imagingapplications, both of the above addressing modes may be used in analternating (i.e., multiplexed) manner, using the same sensor array. Inalternative implementations, depth and brightness images may be acquiredby different sensor arrays, with corresponding pixel positions in thebrightness and depth images identified according to a camera model.

The phase-discriminating ToF camera described above is one of severalToF implementations envisaged herein. Other configurations may includetwo or more sensor elements imaging the same locus of the subject. Eachsensor element may include one or more finger gates, transfer gatesand/or collection nodes. The sensor elements associated with each locusmay be addressed so as to provide two or more integration periodssynchronized to the modulated emission, the integration periodsdiffering in phase and/or total integration time. Based on the relativeamount of charge accumulated on the sensor elements during the differentintegration periods, the distance out to the reflecting locus of thesubject may be obtained. In one, non-limiting example, the emitter and afirst sensor element may be energized synchronously, while a secondsensor element is energized 180° out of phase with respect to the firstsensor element.

As noted above, image data from any ToF camera may be prone to error dueto multipath interference. This issue is illustrated with reference toFIGS. 2A and 2B, which show aspects of an example subject 16′. Thesubject, in this case, is a pair of geometric solids that include afirst area 34 and an adjacent second area 36. Both the first and secondareas are planar surfaces parallel to the vertical Y axis. The first andsecond areas are set at an angle to each other, extending farthest alongthe depth axis Z in the region where they approach each other. In thisexample, the first area may be highly reflective of the probe light frommodulated emitter 32. In other words, when illuminated by the probelight, first area 34 may reflect such light onto second area 36. In FIG.2A, the configuration and orientation of subject 16′ are chosen merelyto simplify the discussion hereinafter; no aspect of the configurationor orientation are in any way limiting. FIG. 2B shows subject 16 in planview, together with aspects of camera 10—emitter 32, sensor array 14,and electronic controller 28.

The depth-sensing approach described above gives reliable results undersome conditions, but is prone to significant measurement error underother conditions. One source of error is indirect reflection of theprobe light. In FIG. 2B, the desired light path for assessing the depthof locus B is the two-segment path ABC. However, numerous other pathsmay also result in probe light reaching photodetector 20 along rayBC-among them the three-segment paths ADBC and AEBC. Light reflectedalong a three-segment path is received at a larger-than-expected phaseangle, which erroneously lengthens the measured depth of locus B.

In the illustrated example, indirect reflection is a consequence of theorientation of first area 34 relative to second area 36, which defines aconcavity. Although reflection along any three-segment path willtypically be less intense than the direct, two-segment reflection,various factors may increase the significance of indirect reflection asa noise source. For instance, if first area 34 is significantlyreflective of the probe light, then the amount and angular content ofthe indirect reflection may be increased. Naturally, the larger the sizeof first area 34, the greater will be the amount of indirectly reflectedlight that reaches sensor array 14 along BC.

The range of depth-imaging systems envisaged herein extends beyond ToFcameras; it includes stereoscopic and structured-light cameras as well.In stereo implementations, brightness or color data from separatedsensor arrays are co-registered and used to construct a depth image.More generally, depth coordinates into any scene may be obtained usingone or more brightness-imaging cameras, with optical-tomography basedco-registration of imaged features. Hyperspectral (e.g., visible+IRand/or UV) brightness imaging may be used with this approach, forimproved feature discrimination. In structured-light examples, an IRillumination source associated with a depth-imaging camera may beconfigured to project onto the subject an illumination patterncomprising numerous discrete features—e.g., lines or dots. A sensorarray in the depth-imaging camera may be configured to image thestructured illumination reflected back from the subject. Based on thespacings between adjacent features in the various regions of the imagedsubject, a depth image of the subject may be constructed.

As noted hereinabove, camera 10 may be integrated into a more complexdevice or system. FIGS. 3, 4, and 5 show example systems each having anintegrated depth-imaging camera. Each of the illustrated systems mayembody a virtual, three-dimensional modeling system 38, shownschematically in FIG. 3. The modeling system includes the depth-imagingcamera 10, operatively coupled to a modeling computer 40 via a wired orwireless hardware interface 42. The modeling computer is alsooperatively coupled to an optional non-imaging sensor unit 44, which mayinclude an inertial measurement unit (IMU) or global positioning-system(GPS) receiver. The modeling computer includes computer memory machine46 and at least one logic machine 48. The computer memory machine mayhold instructions that cause the logic machine(s) to enact variousaspects of virtual, three-dimensional modeling, including the methodsdisclosed further below. Additional aspects of the modeling computer aredescribed hereinafter.

FIG. 3 also shows, more specifically, a smartphone 50 with a modelingcomputer 40A and depth-imaging camera 10A arranged behind display bezel52. FIG. 4 shows a home-theatre system 54 with peripheral modelingcomputer 40B and depth-imaging camera 10B. FIG. 5 shows a head-mountedaugmented-reality display system 56 having an integrated modelingcomputer 40C and depth-imaging camera 10C. Each of these systems mayalso include an optional non-imaging sensor unit, not shown in thedrawings.

FIG. 6 illustrates aspects of an example method 58 for virtual,three-dimensional modeling of a subject 16, using a virtual,three-dimensional modeling system. The modeling system may include adepth-imaging camera 10 operatively coupled to a modeling computer 40,as described above. In other implementations, the method may be enactedby an different modeling system. Method 58 describes, in addition tovirtual, three-dimensional modeling of the imaged subject, optionalsupportive features of invalidating depth imagery that may be corruptedby multipath interference and/or correcting the corrupted depth imagery.In other implementations, the invalidating/corrective features can beused independent of the three-dimensional modeling aspect. Although FIG.6 illustrates an example ordering of the various acts of the method, itwill be understood that some of the features may be executed in adifferent order, or in parallel. In the following description, thevarious acts and features of the method are presented for clarity ofillustration and numbered in that order, which is not necessarily theorder of execution.

At the outset of method 58, coordinate images captured by depth-imagingcamera 10 are received through hardware interface 42 of modelingcomputer 40. More specifically, at 60 a brightness image of subject 16including a relative brightness value for each of a plurality of pixelpositions is received from the camera, and at 62 a depth image of thesubject including a depth value for each of a plurality of pixelpositions is received from the camera. The term ‘coordinate’ emphasizesthat the brightness image and its companion depth image are captured atsubstantially the same moment in time—i.e., concurrently or immediatelysuccessively based on depth to brightness transition rate. Furthermore,coordinate brightness and depth images may overlap, such that at leastsome pixel positions of the brightness image may be registeredalgorithmically to corresponding pixel positions of the coordinate depthimage, and vice versa.

Between successive executions of 60 and 62, the relative position and/ororientation of camera 10 versus subject 16 may be changed. Accordingly,as coordinate brightness and depth images are captured again and again,the subject may be sighted by the camera from a plurality ofinequivalent vantage points. A ‘vantage point,’ as used herein, may bedefined by the aperture position X₀, Y₀, Z₀ of the camera and any otherpoint that, together with the aperture position, defines the opticalaxis of the camera—e.g., a point X₁, Y₁, Z₁ located a predetermineddistance in front of the camera aperture, along the optical axis. Changein the relative position and/or orientation of the camera may berealized by movement of the camera, by movement of the subject, or bymovement of both the camera and the subject. In this manner, thecoordinate brightness and depth images received by the modeling computerat 60 and 62 may be images captured from a plurality of inequivalentvantage points, the vantage points differing in relative position and/ororientation of the camera versus the subject. FIG. 7 shows aspects of anexample subject being imaged by a moving camera, imaging a plurality ofloci 64. Naturally, this variant is realized more conveniently using awearable or handheld camera or camera-enabled device.

Returning now to FIG. 6, at 66 of method 58, modeling computer 40 parsesdata from various depth images acquired from one or more of the vantagepoints in order to construct a virtual, three-dimensional model ofsubject 16. The model is held in computer memory machine 46 of themodeling computer. In some implementations, image capture from differentvantage points serves to resolve subject features and surfaces that maybe occluded from a single vantage point. As the depth-imaging cameramoves through the scene, various loci of the subject may be recognizedand recorded in order to estimate the changing position and/ororientation of the camera versus the subject (vide infro). A locus ofthe subject resolved in this manner may also be referred to as a‘feature patch.’

At 68 of method 58, modeling computer 40 determines (e.g.,computationally or via a look-up table) an angle-dependent reflectancefor each of a plurality of loci of the subject. The angle-dependentreflectance is computed based on the coordinate brightness and depthimages acquired from each of the plurality of vantage points that thecamera moves through. In some implementations, the angle dependentreflectance R may be a vector-valued function having a horizontalcomponent R_(H) and a vertical component R_(V). Each of the horizontaland vertical components of the reflectance may be functions of anincidence angle α and/or an observation angle β defined relative tohorizontal or vertical planes. In other implementations, theangle-dependent reflectance may be a scalar function subsuming bothhorizontal and vertical components or omitting one or the other. Inthese and other implementations, the dependence of the reflectance ontwo different angles, α and β, may be simplified according to certainassumptions (vide infra).

In some implementations, the angle-dependent reflectance R may berepresented in the form of a table of numbers stored in computer memorymachine 46 of modeling computer 40. Each subject locus for which anangle-dependent reflectance is defined may be associated with its owntable. A column (or columns) of the table may represent R (or componentsthereof), evaluated for each of a series of discrete angles, which arerepresented by the rows. Naturally, the modeling computer may beconfigured to interpolate between and/or extrapolate beyond the discretevalues referenced in the table.

In order to evaluate the reflectance of a given locus at each of aplurality of incidence and/or observation angles, that same locus isobserved from a plurality of inequivalent vantage points. Accordingly,one step in the process of accumulating the angle-dependent reflectanceis to correlate various observations of the same locus across pluralbrightness and coordinate depth images captured from different vantagepoints.

The process is one of associating an observed locus of the subject withcorresponding regions of two or more brightness images and of two ormore coordinate depth images, such images being captured from two ormore vantage points. The association may be achieved in various ways,which generally involve correlating image data captured from prior andsubsequent vantage points. One correlation approach is based onrecognizing a common feature in two or more brightness or depth imagescaptured from two or more inequivalent vantage points—e.g., alow-probability brightness pattern in two or more brightness images or alow-probability contour in two or more depth images. It should beunderstood that feature matching need only be realized in either thebrightness images or the depth images, for once a match is detected inone set of images, the same subject locus may be identified in thecoordinate set, via algorithmic registry of the coordinate brightnessand depth images. Another correlation approach is based on estimating inreal time, during image capture, the relative position and/ororientation of the camera versus the subject. For relatively smallsubjects—on the order of centimeters to meters—this can be done usingoutput from an inertial measurement unit (IMU) coupled to the camera.The IMU may include a three-axis accelerometer and three-axis gyroscope,for a combined six degrees-of-freedom (6DOF) measurement. In someimplementations, additional sensor input may be fused with IMU outputfor increased position and/or orientation sensing accuracy. Examplesinclude magnetometer data to provide an absolute orientation, opticalflow from camera 10, etc. For larger subjects, a global-positioningsystem (GPS) receiver may be used.

Once a correlation among regions of two or more brightness images hasbeen established (directly or indirectly), one or more R values may bewritten into the angle-dependent reflectance table for each observationof a locus made from a unique vantage point. To this end, eachbrightness image may be converted into a reflectance map. The conversionmay be such as to compensate for varying illumination intensity, lensshading, and registration between the infrared emitter 32 and aperture12 of depth-imaging camera 10. Conversion of a brightness image into areflectance map may include correction for the geometric fall-off inimaged brightness of each locus of the subject by a factor inverselyproportional to the square of the depth of that locus (1/Z²). The depthof the locus may be obtained from the corresponding region of the depthmap coordinate to the brightness image from which the reflectance map isobtained. In some implementations, the geometric intensity fall-off maybe the only correction applied. From a reflectance map constructed inthis manner, reflectance values may be read from pixel positionscorresponding to those of the parent brightness image, where associationto a subject locus has been made.

In order to determine the angle value(s) corresponding to eachreflectance value, the depth image coordinate to the correctedbrightness image is again applied. In some implementations, the depthimage is processed to estimate a surface-normal vector from each of theplurality of observed loci of the subject. In some implementations, adata pair R, θ may be recorded for each subject locus identified. Thedata pair may relate incidence (θ=α) or observation (θ=β) angle to themeasured reflectivity. In some implementations, θ is defined simply asthe angle that the surface-normal vector makes relative to the opticalaxis of the camera. When the illuminator and imaging optics areapproximately co-localized, typically the case for compact imagingsystems, the R(α, β) function collapses to a simplified, special caseR(θ), in which the incidence and exit angles are equal.

Continuing in FIG. 6, the foregoing steps are continued as the cameramoves about the environment (and/or as the subject moves about thecamera), so as to build up an increasingly complete angle-dependentreflectance table for every locus of the subject. In this manner, abidirectional reflectivity-distribution function (BRDF) may beaccumulated for each of the plurality of loci. FIG. 8 illustrates anexample bidirectional reflectivity distribution function (BRDF), whichmay be constructed over time for every subject locus in the scene.

Returning again to FIG. 6, at 70 of method 58, modeling computer 40assigns a surface attribute, based on the angle-dependent reflectance ofeach of the plurality loci of the subject, to each of a correspondingplurality of loci of the model. In some implementations, the surfaceattribute includes a texture. For example, a smooth texture may beassigned to loci exhibiting a relatively narrow BRDF, and a roughtexture to loci exhibiting a relatively broad BRDF. To quantify therelative breadth of the BRDF for texturization, and/or secure otheradvantages, a specularity metric may be computed at 72 of method 58,based on the angle-dependent reflectance of a given locus of thesubject.

In some implementations, the specularity metric evaluated at a givenlocus of the subject expresses reflectance of the locus at a smaller(near-normal) incidence angle relative to reflectance of the locus at alarger (more glancing) incidence angle. Suitable examples may include 0to 10 degrees for near normal incidence, and 50 to 80 degrees for themore glancing angle. Such metrics estimate the relative specularity ofthe feature patch being scanned. One formula for determining aspecularity metric of a subject locus is illustrated with continuedreference to FIG. 8, wherein identifies the reflectivity of the locusmeasured at zero degrees is compared to the reflectivity measured at 55degrees. In other, examples, the reflectance measured at 5 degrees maybe compared to the reflectance measured at 60 degrees, etc.

In subsequent acts of method 58, modeling computer 40 corrects orinvalidates the depth image acquired from at least one of the vantagepoints based on the angle-dependent reflectance. In someimplementations, the depth image is invalidated pursuant to thespecularity metric exceeding a predetermined threshold. At 74,accordingly, it is determined whether the specularity metric exceeds apredetermined threshold (e.g., 5.0). If the specularity metric exceedsthe threshold, then at 76, any depth map affected by the highspecularity is invalidated.

At 78 modeling computer 40 issues an alert (e.g., an error code)pursuant to invalidation of the depth image. In this manner, the user isalerted that the subject includes a feature of high specularity, and maynot be scanned properly or to high accuracy, or that OCAP may notcomplete successfully. Alternatively, or in addition to alerting theuser, corrective action may be taken, such as attempting to reverse theeffects of the high-specularity feature on the modeling of the subject.More specifically, as the angle-dependent reflectance becomes welldefined over a wide range of angles, accurate multipath correction maybe applied, as described below.

At 80, therefore, a depth image is corrected to compensate for indirectillumination of a first locus of the subject via a second locus, suchthat the indirect illumination is compensated in an amount responsive tothe angle-dependent reflectance of the second locus. In other words,simultaneous knowledge of the normal vector and the angle-dependentreflectance enables correction for multipath depth errors by predictinghow much light must have been reflected from non-occluded subject lociand observed by pixels not associated with such loci.

FIG. 9 provides an illustration of how specular properties of two targetloci can be used to unambiguously predict relative intensity of light onone of the targets from multiple optical paths, thereby allowing a moreaccurate estimation of depth. Solid angle δ represents the volumeobserved by a single pixel. If the angle-dependent reflectance is known,then intensity reflected back to the camera can be predicted from thesurface-normal vectors and from the depth-image stream.

The methods and processes described herein may be tied to a computingsystem of one or more computing devices. In particular, such methods andprocesses may be implemented as a computer-application program orservice, an application-programming interface (API), a library, and/orother computer-program product.

FIG. 3 schematically shows a non-limiting embodiment of a computingsystem in the form of modeling computer 40 that can enact one or more ofthe methods and processes described above. The modeling computer isshown in simplified form in FIG. 3. The modeling computer may take theform of one or more personal computers, server computers, tabletcomputers, home-entertainment computers, network computing devices,gaming devices, mobile computing devices, mobile communication devices(e.g., smart phone), and/or other computing devices.

The modeling computer includes a logic machine 48 and a computer memorymachine 46. The modeling computer may optionally include a displaysubsystem, an input subsystem, a communication subsystem, and/or othercomponents not shown in FIG. 3.

Logic machine 48 includes one or more physical devices configured toexecute instructions. For example, the logic machine may be configuredto execute instructions that are part of one or more applications,services, programs, routines, libraries, objects, components, datastructures, or other logical constructs. Such instructions may beimplemented to perform a task, implement a data type, transform thestate of one or more components, achieve a technical effect, orotherwise arrive at a desired result.

The logic machine may include one or more processors configured toexecute software instructions. Additionally or alternatively, the logicmachine may include one or more hardware or firmware logic machinesconfigured to execute hardware or firmware instructions. Processors ofthe logic machine may be single-core or multi-core, and the instructionsexecuted thereon may be configured for sequential, parallel, and/ordistributed processing. Individual components of the logic machineoptionally may be distributed among two or more separate devices, whichmay be remotely located and/or configured for coordinated processing.Aspects of the logic machine may be virtualized and executed by remotelyaccessible, networked computing devices configured in a cloud-computingconfiguration.

Computer memory machine 46 includes one or more physical devicesconfigured to hold instructions executable by the logic machine toimplement the methods and processes described herein. When such methodsand processes are implemented, the state of computer memory machine 46may be transformed—e.g., to hold different data.

Computer memory machine 46 may include removable and/or built-indevices. Computer memory machine 46 may include optical memory (e.g.,CD, DVD, HD-DVD, Blu-Ray Disc, etc.), semiconductor memory (e.g., RAM,EPROM, EEPROM, etc.), and/or magnetic memory (e.g., hard-disk drive,floppy-disk drive, tape drive, MRAM, etc.), among others. Computermemory machine 46 may include volatile, nonvolatile, dynamic, static,read/write, read-only, random-access, sequential-access,location-addressable, file-addressable, and/or content-addressabledevices.

It will be appreciated that computer memory machine 46 includes one ormore physical devices. However, aspects of the instructions describedherein alternatively may be propagated by a communication medium (e.g.,an electromagnetic signal, an optical signal, etc.) that is not held bya physical device for a finite duration.

Aspects of logic machine 48 and computer memory machine 46 may beintegrated together into one or more hardware-logic components. Suchhardware-logic components may include field-programmable gate arrays(FPGAs), program- and application-specific integrated circuits(PASIC/ASICs), program- and application-specific standard products(PSSP/ASSPs), system-on-a-chip (SOC), and complex programmable logicdevices (CPLDs), for example.

The terms ‘module,’ ‘program,’ and ‘engine’ may be used to describe anaspect of the modeling computer implemented to perform a particularfunction. In some cases, a module, program, or engine may beinstantiated via logic machine 48 executing instructions held bycomputer memory machine 46. It will be understood that differentmodules, programs, and/or engines may be instantiated from the sameapplication, service, code block, object, library, routine, API,function, etc. Likewise, the same module, program, and/or engine may beinstantiated by different applications, services, code blocks, objects,routines, APIs, functions, etc. The terms ‘module,’ ‘program,’ and‘engine’ may encompass individual or groups of executable files, datafiles, libraries, drivers, scripts, database records, etc.

It will be appreciated that a ‘service’, as used herein, is anapplication program executable across multiple user sessions. A servicemay be available to one or more system components, programs, and/orother services. In some implementations, a service may run on one ormore server-computing devices.

When included, a display subsystem of the modeling computer may be usedto present a visual representation of data held by computer memorymachine 46. This visual representation may take the form of a graphicaluser interface (GUI). As the herein described methods and processeschange the data held by the computer memory machine, and thus transformthe state of the computer memory machine, the state of the displaysubsystem may likewise be transformed to visually represent changes inthe underlying data. The display subsystem may include one or moredisplay devices utilizing virtually any type of technology. Such displaydevices may be combined with logic machine 48 and/or computer memorymachine 46 in a shared enclosure, or such display devices may beperipheral display devices.

When included, an input subsystem of the modeling computer may compriseor interface with one or more user-input devices such as a keyboard,mouse, touch screen, or game controller. In some embodiments, the inputsubsystem may comprise or interface with selected natural user input(NUI) componentry. Such componentry may be integrated or peripheral, andthe transduction and/or processing of input actions may be handled on-or off-board. Example NUI componentry may include a microphone forspeech and/or voice recognition; an infrared, color, stereoscopic,and/or depth camera for machine vision and/or gesture recognition; ahead tracker, eye tracker, accelerometer, and/or gyroscope for motiondetection and/or intent recognition.

When included, a communication subsystem of the modeling computer may beconfigured to communicatively couple the modeling computer with one ormore other computing devices. The communication subsystem may includewired and/or wireless communication devices compatible with one or moredifferent communication protocols. As non-limiting examples, thecommunication subsystem may be configured for communication via awireless telephone network, or a wired or wireless local- or wide-areanetwork. In some embodiments, the communication subsystem may allow thecomputing system to send and/or receive messages to and/or from otherdevices via a network such as the Internet.

Aspects of this disclosure are described by example, and with referenceto the attached drawing figures. Components, process steps, and otherelements that may be substantially the same in one or more of thefigures are identified coordinately and are described with minimalrepetition. It will be noted, however, that elements identifiedcoordinately may also differ to some degree. It will be further notedthat the figures are schematic not necessarily drawn to scale. Rather,the various drawing scales, aspect ratios, and numbers of componentsshown in the figures may be purposely distorted to make certain featuresor relationships easier to see.

One aspect of this disclosure provides a method for virtual,three-dimensional modeling of a subject using a depth-imaging cameraoperatively coupled to a modeling computer. The method comprises: withthe modeling computer, receiving from the depth-imaging camera abrightness image and a coordinate depth image of the subject acquiredfrom each of a plurality of inequivalent vantage points relative to thesubject, the brightness image including a brightness value for each of aplurality of pixel positions, the coordinate depth image including adepth value for each of a plurality of pixel positions; in the modelingcomputer, parsing data from depth images acquired from one or more ofthe inequivalent vantage points to construct a virtual,three-dimensional model of the subject; determining with the modelingcomputer, for each of a plurality of loci of the subject, anangle-dependent reflectance based on the brightness and coordinate depthimages received from the depth-imaging camera; and with the modelingcomputer, assigning a surface attribute, based on the angle-dependentreflectance of each of the plurality loci of the subject, to each of acorresponding plurality of loci of the model.

In some implementations, the surface attribute includes a texture. Insome implementations, the method further comprises changing a relativeposition and/or orientation of the depth-imaging camera versus thesubject, such that the subject is sighted by the depth-imaging camerafrom each of the plurality of inequivalent vantage points.

Another aspect of this disclosure provides a method for virtual,three-dimensional modeling of a subject using a depth-imaging cameraoperatively coupled to a modeling computer. The method comprises: withthe modeling computer, receiving from the depth-imaging camera abrightness image and a coordinate depth image of the subject acquiredfrom each of a plurality of inequivalent vantage points relative to thesubject, the brightness image including a brightness value for each of aplurality of pixel positions, the coordinate depth image including adepth value for each of a plurality of pixel positions; determining withthe modeling computer, for each of a plurality of loci of the subject,an angle-dependent reflectance based on the brightness and coordinatedepth images received from the depth-imaging camera; and with themodeling computer, correcting or invalidating the depth image acquiredfrom at least one of the inequivalent vantage points based on theangle-dependent reflectance.

In some implementations, determining the angle-dependent reflectanceincludes registering incidence and reflection angle from each of theplurality of loci of the subject to reflectance at that locus. In someimplementations, determining the angle-dependent reflectance includesaccumulating a bidirectional reflectivity-distribution function for eachof the plurality of loci of the subject. In some implementations,determining the angle-dependent reflectance includes processing a depthimage to estimate a surface-normal vector for each of the plurality ofloci of the subject. In some implementations, determining theangle-dependent reflectance includes associating a given subject locusof the subject with corresponding regions of two or more brightnessimages and with corresponding regions of two or more coordinate depthimages. In some implementations, associating the given locus of thesubject with corresponding regions of two or more brightness images andwith corresponding regions of two or more coordinate depth imagesincludes correlating prior and subsequent vantage points. In someimplementations, associating the given locus of the subject withcorresponding regions of two or more brightness images and withcorresponding regions of two or more coordinate depth images includesrecognizing a common feature in brightness or coordinate depth imagesfrom two or more inequivalent vantage points. In some implementations,associating the given locus of the subject with corresponding regions oftwo or more brightness images and with corresponding regions of two ormore coordinate depth images includes estimating a relative positionand/or orientation of the depth-imaging camera versus the subject basedon output of an inertial measurement unit coupled to the depth-imagingcamera. In some implementations, determining the angle-dependentreflectance includes converting a brightness image into a reflectancemap. In some implementations, conversion of the brightness image into areflectance map compensates for one or more of illumination intensity,lens shading, and registration between an infrared emitter and anaperture of the depth-imaging camera. In some implementations,conversion of the brightness image into a reflectance map includescorrection for a geometric fall-off in imaged brightness from each locusof the subject by a factor inversely proportional to a square of a depthof that locus. In some implementations, correcting or invalidating thedepth image includes invalidating the depth image pursuant to aspecularity metric exceeding a threshold, the method further comprisingdetermining the specularity metric based on the angle-dependentreflectance of a locus of the subject. In some implementations, themethod further comprises issuing an alert pursuant to invalidation ofthe depth image. In some implementations, the specularity metricevaluated at a given locus of the subject expresses reflectance of thelocus at a smaller incidence angle relative to reflectance of the locusat a larger incidence angle. In some implementations, correcting orinvalidating the depth image includes correcting the depth image tocompensate for indirect illumination of a first locus of the subject viaa second locus of the subject, such that the indirect illumination iscompensated in an amount responsive to the angle-dependent reflectanceof the second locus of the subject.

Another aspect of this disclosure provides a virtual, three-dimensionalmodeling system comprising: a hardware interface configured to receive,from a depth-imaging camera, a brightness image and a coordinate depthimage of the subject acquired from each of a plurality of inequivalentvantage points relative to the subject, the brightness image including abrightness value for each of a plurality of pixel positions, thecoordinate depth image including a depth value for each of a pluralityof pixel positions; a computer memory machine configured to hold avirtual, three-dimensional model of the subject; logic operativelycoupled to the computer memory machine, including: logic to parse datafrom depth images acquired from one or more of the inequivalent vantagepoints to construct a virtual, three-dimensional model of the subject inthe machine-readable memory, logic to determine, for each of a pluralityof loci of the subject, an angle-dependent reflectance based on thebrightness and coordinate depth images received from the depth-imagingcamera, and logic to assign a surface attribute, based on theangle-dependent reflectance of each of the plurality loci of thesubject, to each of a corresponding plurality of loci of the model.

In some implementations, the depth-imaging camera is a time-of-flightcamera including a modulated infrared emitter configured to illuminatethe subject.

It will be understood that the configurations and/or approachesdescribed herein are exemplary in nature, and that these specificembodiments or examples are not to be considered in a limiting sense,because numerous variations are possible. The specific routines ormethods described herein may represent one or more of any number ofprocessing strategies. As such, various acts illustrated and/ordescribed may be performed in the sequence illustrated and/or described,in other sequences, in parallel, or omitted. Likewise, the order of theabove-described processes may be changed.

The subject matter of the present disclosure includes all novel andnonobvious combinations and subcombinations of the various processes,systems and configurations, and other features, functions, acts, and/orproperties disclosed herein, as well as any and all equivalents thereof.

The invention claimed is:
 1. A method for virtual, three-dimensionalmodeling of a subject using a depth-imaging camera operatively coupledto a modeling computer, the method comprising: with the modelingcomputer, receiving from the depth-imaging camera a brightness image anda coordinate depth image of the subject acquired from each of aplurality of inequivalent vantage points relative to the subject, thebrightness image including a brightness value for each of a plurality ofpixel positions, the coordinate depth image including a depth value foreach of a plurality of pixel positions; in the modeling computer,parsing data from depth images acquired from one or more of theinequivalent vantage points to construct a virtual, three-dimensionalmodel of the subject; determining with the modeling computer, for eachof a plurality of loci of the subject, an angle-dependent reflectancebased on the brightness and coordinate depth images received from thedepth-imaging camera; and with the modeling computer, assigning asurface attribute, based on the angle-dependent reflectance of each ofthe plurality loci of the subject, to each of a corresponding pluralityof loci of the model.
 2. The method of claim 1 wherein the surfaceattribute includes a texture.
 3. The method of claim 1 furthercomprising changing a relative position and/or orientation of thedepth-imaging camera versus the subject, such that the subject issighted by the depth-imaging camera from each of the plurality ofinequivalent vantage points.
 4. A method for virtual, three-dimensionalmodeling of a subject using a depth-imaging camera operatively coupledto a modeling computer, the method comprising: with the modelingcomputer, receiving from the depth-imaging camera a brightness image anda coordinate depth image of the subject acquired from each of aplurality of inequivalent vantage points relative to the subject, thebrightness image including a brightness value for each of a plurality ofpixel positions, the coordinate depth image including a depth value foreach of a plurality of pixel positions; determining with the modelingcomputer, for each of a plurality of loci of the subject, anangle-dependent reflectance based on the brightness and coordinate depthimages received from the depth-imaging camera; and with the modelingcomputer, correcting or invalidating the depth image acquired from atleast one of the inequivalent vantage points based on theangle-dependent reflectance.
 5. The method of claim 4 whereindetermining the angle-dependent reflectance includes registeringincidence and reflection angle from each of the plurality of loci of thesubject to reflectance at that locus.
 6. The method of claim 4 whereindetermining the angle-dependent reflectance includes accumulating abidirectional reflectivity-distribution function for each of theplurality of loci of the subject.
 7. The method of claim 4 whereindetermining the angle-dependent reflectance includes processing a depthimage to estimate a surface-normal vector for each of the plurality ofloci of the subject.
 8. The method of claim 4 wherein determining theangle-dependent reflectance includes associating a given subject locusof the subject with corresponding regions of two or more brightnessimages and with corresponding regions of two or more coordinate depthimages.
 9. The method of claim 8 wherein associating the given locus ofthe subject with corresponding regions of two or more brightness imagesand with corresponding regions of two or more coordinate depth imagesincludes correlating prior and subsequent vantage points.
 10. The methodof claim 8 wherein associating the given locus of the subject withcorresponding regions of two or more brightness images and withcorresponding regions of two or more coordinate depth images includesrecognizing a common feature in brightness or coordinate depth imagesfrom two or more inequivalent vantage points.
 11. The method of claim 8wherein associating the given locus of the subject with correspondingregions of two or more brightness images and with corresponding regionsof two or more coordinate depth images includes estimating a relativeposition and/or orientation of the depth-imaging camera versus thesubject based on output of an inertial measurement unit coupled to thedepth-imaging camera.
 12. The method of claim 4 wherein determining theangle-dependent reflectance includes converting a brightness image intoa reflectance map.
 13. The method of claim 12 wherein conversion of thebrightness image into a reflectance map compensates for one or more ofillumination intensity, lens shading, and registration between aninfrared emitter and an aperture of the depth-imaging camera.
 14. Themethod of claim 12 wherein conversion of the brightness image into areflectance map includes correction for a geometric fall-off in imagedbrightness from each locus of the subject by a factor inverselyproportional to a square of a depth of that locus.
 15. The method ofclaim 4 wherein correcting or invalidating the depth image includesinvalidating the depth image pursuant to a specularity metric exceedinga threshold, the method further comprising determining the specularitymetric based on the angle-dependent reflectance of a locus of thesubject.
 16. The method of claim 4 further comprising issuing an alertpursuant to invalidation of the depth image.
 17. The method of claim 4wherein the specularity metric evaluated at a given locus of the subjectexpresses reflectance of the locus at a smaller incidence angle relativeto reflectance of the locus at a larger incidence angle.
 18. The methodof claim 4 wherein correcting or invalidating the depth image includescorrecting the depth image to compensate for indirect illumination of afirst locus of the subject via a second locus of the subject, such thatthe indirect illumination is compensated in an amount responsive to theangle-dependent reflectance of the second locus of the subject.
 19. Avirtual, three-dimensional modeling system comprising: a hardwareinterface configured to receive, from a depth-imaging camera, abrightness image and a coordinate depth image of the subject acquiredfrom each of a plurality of inequivalent vantage points relative to thesubject, the brightness image including a brightness value for each of aplurality of pixel positions, the coordinate depth image including adepth value for each of a plurality of pixel positions; a computerprocessor; a computer memory machine operatively coupled to the computerprocessor and configured to hold electronically a virtual,three-dimensional model of the subject, together with instructionsexecutable on the computer processor, the instructions including:instructions to parse data from depth images acquired from one or moreof the inequivalent vantage points to construct a virtual,three-dimensional model of the subject in the machine-readable memory,instructions to determine, for each of a plurality of loci of thesubject, an angle-dependent reflectance based on the brightness andcoordinate depth images received from the depth-imaging camera, andinstructions to assign a surface attribute, based on the angle-dependentreflectance of each of the plurality loci of the subject, to each of acorresponding plurality of loci of the model.
 20. The modeling system ofclaim 19 wherein the depth-imaging camera is a time-of-flight cameraincluding a modulated infrared emitter configured to illuminate thesubject.